The present invention relates to a cable sleeve system for bone fixation, and in particular to a cable sleeve system comprising a sleeve consisting of a head and a piercing portion, and a cable. The cable sleeve system of the present invention is useful in the treatment of fractures in the femoral greater trochanter, olecranon, tibial tubercle and medial malleolus of the ankle, and in bone fixation following cutting operations involving such bone parts.
Cases of osteoporosis are becoming increasingly common with the progress in the aging of the population, and this is in turn leading to an increasing number of cases requiring hip joint replacement such as hip joint fractures, coxarthrosis, and femoral head necrosis. Also, knee joint replacement is becoming increasingly common due to the increase in the cases of gonarthrosis. In particular, it is often necessary to cut off the greater trochanter in the case of a hip joint replacement operation, and to cut off the tibial tubercule in the case of a knee joint replacement, to gain access to the joint in either case. The separated bone part needs to be restored to the original state once the operation on the joint is completed. This is normally accomplished by the bone fixation method using screws, the bone fixation method bused on cable tensioning by using pins and a mild steel cable, or the bone fixation method using a cable grip and cable.
However, the methods based on the use of screws, pins and spikes are known to have problems because the fixation capability may be lost due to the loosening or breaking of the screws, pins and spikes, and the breaking of the mild steel cable. In case of the bone fixation method using a cable grip and cable, pain and inflammation in the tensor fascia lata muscle and bursa subcutanea trochanterica due to the presence of the cable grip may occur, and this is aggravated by the irritation of the soft body tissues by the cut ends of the cable. Should such an undesirable symptom develop, a reoperation would become necessary, and this would impose a serious burden on the patient. Also, because a bone fixation fixture is an foreign object which is embedded in the human body, it is desired to be as small as possible.
The present invention was made with the aim to resolve such problems of the prior art, and its primary object is to provide a cable sleeve system for bone fixation, comprising a cable, and a sleeve including a head for securing the cable and a piercing portion, wherein the piercing portion projects from a bottom face of the head substantially perpendicularly therefrom, and the head is provided with a bore extending in parallel with the bottom face for securing the cable therein, the head being adapted to be crimped to secure the cable therein.
The sleeve according to the present invention comprises a head and a piercing portion, and may be additionally provided with a grip portion. The upper and lower faces of the head are defined by planes which are parallel to each other, and the head may have any desired shape, such as circular and polygonal shapes, but preferably has a rectangular shape in view of the ease of holding the head and securing the cable. In this case also, sharp corners should be appropriately chamfered so as to minimize irritations to the human body tissues. For the ease of handling the sleeve at the time of driving the piercing portion into the bone, normally, the top face of the head should be larger than the bottom face thereof. As a result, the longitudinal section of the head will have a trapezoidal shape.
The piercing portion is adapted to be driven into the bone and embedded therein, and has a tapered and pointed tip so as to be directly driven into the bone or drilled into the bone by using a drill which is operated either manually or by power. The piercing portion consists of a pin or spikes. In the case of a pin, it typically projects substantially centrally and perpendicularly from the bottom face of the head. The pin includes a part of a relatively constant thickness located adjacent to the head and an end part which is tapered and pointed. The spikes are typically paired on either end of the head, and are each generally tapered and provided with a pointed end.
The sleeve head is provided with a bore for securing the cable therein. The cable fixation bore may consist of a pair of circular bores or a single bore having a cross section in the shape of numeral 8, in each case, extending linearly across the head in parallel with the bottom face of the head. The cable fixation bore is used for securing the cable therein under a prescribed tension for the purpose of firmly closing the fracture plane or cut plane of the bone part at a prescribed pressure.
The sleeve according to the present invention may be provided with a sleeve grip portion which extends centrally from the top face of the sleeve in the opposite direction from the piercing portion. The sleeve grip portion allows the sleeve to be held by hand in a stable manner when driving the piercing portion of the sleeve into the bone part, and is highly useful in simplifying the accurate position of the sleeve on the bone part. The length of the grip portion should be selected for each specific application, and is preferably in the range of about 5 to 10 cm in the case of a greater trochanter fixation. Once the pin is fully pierced into the bone part, and the cable is firmly secured, the sleeve grip portion is not necessary any more. Therefore, it is preferable to provide a notch in the grip portion so that the grip portion may be readily broken by hand at a part immediately above the sleeve without requiring any cutting tool.
The sleeve of the present invention may be made of ceramic materials such as hydroxyapatite, alumina, carbon, calcium phosphate, bioglass, crystallized glass, zirconia, silicon nitride and titanium oxide, metallic materials such as stainless steel, cobalt-chromium alloy, titanium, titanium alloy and tantalum, and polymer materials such as polymethyl-methacrylate, polysulfone, high density polyethylene and polylactic resins. From the viewpoint of mechanical strength, biocompatibility, corrosion resistance and durability cobalt-chromium alloy, titanium, titanium alloy and stainless steel are preferred. Titanium and titanium alloy are particularly preferred from the viewpoint of biocompatibility, corrosion resistance, resiliency, weight and handling. Stainless steel is preferred from the viewpoint of mechanical strength and securing capability. The cable used in the present invention may consist of any material as long as it has required flexibility, tensile strength and biocompatibility, but is preferably made of cobalt-chromium alloy, titanium, titanium alloy or stainless steel, and is more preferably made of the same material as the sleeve from the viewpoint of corrosion in the living body.